How is that annual 50k USD monitored/enforced now? If I have multiple bank accounts, will I be prevented from withdrawing a combined 50k from overseas ATMs?
I think you may ask for a higher limit but usually you just use family accounts.
Paying with a multi-currency credit card has nothing to do with this limit.
In your example, if you have RMB in your China bank account and withdraw RMB overseas, these are no currency exchanges at all. It's not relevant to the $50k exchange cap.